Abstract: A mammal is provided, in which the LKB1 gene can be deleted phase-specifically and tissue-specifically. These mammals are highly useful as tools to reveal the onset mechanism for diseases caused by LKB1 gene deficiency, such as Peutz-Jeghers syndrome and cancers, as well as to develop therapeutic agents, methods, and so on for the diseases.

Abstract: A method for producing biologically active serine proteases, isolated serine protease domains and their amino acid variants in a prokaryotic host is disclosed. The method comprises an N-terminal addition of a helper sequence consisting of a dipeptide which is suitable for degradation by a dipeptidyl amino peptidase, by the expression of the serine protease(s) and/or its (their) fragments containing the N-terminal dipeptide helper sequence, optionally as inclusion bodies, and by the renaturation of the expressed proteins and the activation of the serine protease(s) and/or serine protease domains by splitting off the helper sequence using an exopeptidase.